The invention relates to safety closures for containers of dangerous or harmful contents. To prevent access to contents by young children, removal of such closures requires purposeful manipulation in addition to mere rotation of the closure. One type of safety closure has a top panel and a depending annular skirt. The interior of the skirt is threaded to engage corresponding threads on the exterior of the container neck. The interior of the closure has one or more projecting locking lugs, which engage one or more corresponding locking lugs on the exterior of the container neck. Engagement of the locking lugs prevents the normal rotation necessary to remove the threaded closure from the container. Removal is possible only when the skirt is squeezed and distorted to force the closure locking lugs radially outward from engagement with the neck locking lugs.
Such safety closures, called "squeeze and turn" caps, are known in the prior art. U.S. Pat. Nos. 3,941,268 to Owens, et al. and 4,117,945 to Mumford disclose safety closures and containers which require that the closure be squeezed to disengage locking lugs while the closure is rotated. To form a liquid seal, a compressible liner within the cap has been employed. An effective liquid seal on such prior art closures is achieved when the closure is snugly threadably engaged on the container neck, thereby compressing the liner. To assure both such snug engagement and operation of the locking feature, the threads and lugs must be so aligned in manufacture that after the engagement of the locking lugs the closure may be rotated some small additional increment to finally tighten the closure. To eliminate the necessity for manufacturing precision, a squeeze and turn safety closure whose primary seal does not depend on final rotational orientation of closure to container is obviously desirable.